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Abstract:

An image forming apparatus includes a first image carrier that carries a
first latent image. A first charging section charges the first image
carrier. A first exposure section exposes the first image carrier charged
by the first charging section. A first developing section develops the
first latent image formed on the first image carrier in the first
exposure section using a first liquid developer containing a carrier and
first toner particles. A first primary transfer section transfers a first
image developed in the first developing section onto a transfer medium. A
second image carrier carries a second latent image. A second charging
section charges the second image carrier. A second exposure section
exposes the second image carrier charged by the second charging section.

Claims:

1. An image forming apparatus comprising:a first image carrier that
carries a first latent image;a first charging section that charges the
first image carrier;a first exposure section that exposes the first image
carrier charged by the first charging section;a first developing section
that develops the first latent image formed on the first image carrier in
the first exposure section using a first liquid developer containing a
carrier and first toner particles;a first primary transfer section that
transfers a first image developed in the first developing section onto a
transfer medium;a second image carrier that carries a second latent
image;a second charging section that charges the second image carrier;a
second exposure section that exposes the second image carrier charged by
the second charging section;a second developing section that develops the
second latent image formed on the second image carrier in the second
exposure section using a second liquid developer containing the carrier
and second toner particles;a second primary transfer section that
transfers a second image developed in the second developing section onto
a transfer medium;a carrier removal section of the transfer medium that
removes the carrier from the first and second images transferred on the
transfer medium;a condition storage section that stores a first condition
in which the carrier removal amount in the carrier removal section of the
transfer medium is set to a first carrier removal amount and a second
condition in which the carrier removal amount in the carrier removal
section of the transfer medium is set to a second carrier removal amount
smaller than the first carrier removal amount;an optical sensor that
detects the first and second images transferred on the transfer medium,
from which the carrier has been removed under the first condition stored
in the condition storage section; anda distance calculation section that
calculates the distance between the first and second images detected by
the optical sensor.

2. The image forming apparatus according to claim 1, whereinthe carrier
removal section of the transfer medium is a roller, andthe rotation
direction of the roller differs between the first and second conditions.

3. The image forming apparatus according to claim 1, comprising a second
carrier removal section of the transfer medium that removes a carrier
from the first image transferred on the transfer medium.

4. An image forming apparatus comprising:a first image carrier that
carries a first latent image;a first charging section that charges the
first image carrier;a first exposure section that exposes the first image
carrier charged by the first charging section;a first developing section
that develops the first latent image formed on the first image carrier in
the first exposure section using a first liquid developer containing a
carrier and first toner particles;a carrier removal section of the first
image carrier that removes the carrier from a first image developed in
the first developing section;a first primary transfer section that
transfers the first image from which the carrier has been removed in the
carrier removal section of the first image carrier onto a transfer
medium;a second image carrier that carries a second latent image;a second
charging section that charges the second image carrier;a second exposure
section that exposes the second image carrier charged by the second
charging section;a second developing section that develops the second
latent image formed on the second image carrier in the second exposure
section using a second liquid developer containing the carrier and second
toner particles;a carrier removal section of the second image carrier
that removes the carrier from a second image developed in the second
developing section;a second primary transfer section that transfers the
second image from which the carrier has been removed in the carrier
removal section of the second image carrier onto a transfer medium;a
condition storage section that stores a first condition in which the
carrier removal amount in the carrier removal section of the first image
carrier or the carrier removal section of the second image carrier is set
to a first carrier removal amount and a second condition in which the
carrier removal amount in the carrier removal section of the first image
carrier or the carrier removal section of the second image carrier is set
to a second carrier removal amount smaller than the first carrier removal
amount;an optical sensor that detects the first image transferred on the
transfer medium, from which the carrier has been removed in the carrier
removal section of the first image carrier under the first condition
stored in the condition storage section and second image transferred on
the transfer medium, from which the carrier has been removed in the
carrier removal section of the second image carrier under the first
condition stored in the condition storage section; anda distance
calculation section that calculates the distance between the first and
second images detected by the optical sensor.

5. The image forming apparatus according to claim 4, whereinthe carrier
removal section of the first image carriers is roller, andthe rotation
direction of the roller differs between the first and second conditions.

6. The image forming apparatus according to claim 4, comprising a carrier
removal section of the transfer medium that removes the carrier from the
first and second images transferred on the transfer medium.

7. The image forming apparatus according to claim 4, comprising a second
carrier removal section of the transfer medium that removes the carrier
from the first image transferred on the transfer medium.

8. The image forming apparatus according to claim 4, comprising:a second
carrier removal section of the first image carrier that removes the
carrier from the first image from which the carrier has been removed in
the carrier removal section of the first image carrier; anda second
carrier removal section of the second image carrier that removes the
carrier from the second image from which the carrier has been removed in
the carrier removal section of the second image carrier.

9. The image forming apparatus according to claim 8, whereinthe second
carrier removal section of the first image carrier abuts and separates
thereon from the first image carrier, andthe second carrier removal
section of the second image carrier abuts and separates thereon from the
second image carrier.

10. An image forming apparatus control method, comprising:charging a first
image carrier;exposing the first image carrier charged to form a first
latent image;developing the first latent image formed on the first image
carrier using a first liquid developer containing a carrier and first
toner particles;removing the carrier from a first image developed using
the first liquid developer;transferring the first image from which the
carrier has been removed onto a transfer medium;charging a second image
carrier;exposing the second image carrier charged to form a second latent
image;developing the second latent image formed on the second image
carrier using a second liquid developer containing the carrier and second
toner particles;removing the carrier from a second image developed using
the second liquid developer;transferring the second image from which the
carrier has been removed onto a transfer medium; andperforming image
formation on a first recording medium under a first condition in which
the carrier removal amount in the first image carrier or the second image
carrier is set to a first carrier removal amount, while performing image
formation on a second recording medium having a rougher surface than that
of the first recording medium under a second condition in which the
carrier removal amount in the first image carrier or the second image
carrier is set to a second carrier removal amount smaller than the first
carrier removal amount, whereinwhen detecting the first and second images
transferred on the transfer member and calculating the distance between
the first and second images detected, the first condition is used to
perform image formation.

11. The image forming apparatus control method according to claim 10,
comprising removing the carrier from the first and second images
transferred on the transfer medium.

12. The image forming apparatus control method according to claim 10,
comprising removing the carrier from the first image transferred on the
transfer medium.

13. The image forming apparatus control method according to claim 10,
comprising:removing the carrier from the first image from which the
carrier has been removed in the first image carrier; andremoving the
carrier from the second image from which the carrier has been removed in
the second image carrier.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]This application is based upon and claims the benefit of priority
from prior Japanese Patent Applications No. 2007-338910 filed on Dec. 28,
2007 and No. 2008-289429 filed on Nov. 12, 2008, the entire contents of
which are incorporated herein by reference.

1. TECHNICAL FIELD

[0002]The present invention relates to an image forming apparatus that
forms a color image by superposing liquid developer of a plurality of
colors and a control method of the image forming apparatus and, more
particularly, to an image forming apparatus that carries out a transfer
process of transferring a developed image formed on an image carrier onto
a transfer medium such as an intermediate transfer belt for each color
liquid developer to form a color image onto the transfer medium and a
control method of the image forming apparatus.

2. DESCRIPTION OF THE RELATED ART

[0003]There have been proposed various types of wet-developing image
forming apparatuses that develops a latent image using a high-viscosity
liquid developer obtained by dispersing solid toner particles in a
solvent to visualize an electrostatic latent image. A developer used in
this wet-developing image forming apparatus is prepared by suspending
solid content (toner particles) in a high-viscosity electric insulating
organic solvent (carrier liquid) such as a silicon oil, mineral oil, or
edible oil. The toner particles are so micronized as to have a particle
diameter of about 1 μm. By use of such micro toner particles in a
wet-developing image forming apparatus, relatively high quality can be
achieved as compared to a dry-developing image forming apparatus using
toner powder particles having a particle diameter of about 7 μm.

[0004]As an image forming apparatus of such a type, there is known one
disclosed in, e.g., Patent Document 1: JP-A-2006-126258. In this image
forming apparatus, image forming stations of different colors are
arranged along a transfer medium such as a transfer belt. In each image
forming station, a charging unit, an image writing unit, and a developing
unit are arranged around a latent image carrier such as a photosensitive
drum. Toner images formed by the respective image forming stations are
superposed on the transfer medium, whereby a color image is formed.

[0005]Color shift is considered as one of the most serious problem in an
image forming apparatus having a plurality of image forming stations. The
color shift is caused when transfer positions of respective toner images
formed in different image forming stations are relatively shifted from
one another and appears as a change in the color tone. To eliminate this
problem, the following approach is taken: reference pattern images
(hereinafter, referred to as "resist marks") for detecting color shift is
previously formed on a transfer medium; the respective resist marks are
detected using an optical sensor to acquire position information of the
resist marks; and positioning (color shift compensation processing,
displacement compensation processing) of respective toner images are
performed based on the acquired position information.

[0006]The processing of compensating color shift in the image forming
apparatus disclosed in JP-A-2006-126258 is described in connection with
FIG. 12 and the like of the cited document. As shown in FIG. 12, resist
marks YRM (yellow resist mark), MRM (magenta resist mark), CRM (cyan
resist mark), and KRM (black resist mark) are formed, as toner images, in
this order onto an intermediate transfer belt 41 through an ordinary
image forming operation executed immediately after power-on. At this
time, image forming timing is controlled so that the resist marks YRM,
MRM, CRM, and KRM are formed on a reference position S0. However, as
shown in FIG. 12, there is a case where the resist marks MRM, CRM, and
KRM are formed at positions shifted from the reference position S0 by Sm,
Sc, and Sk, respectively, in the scanning direction X of a laser beam due
to an apparatus assembly error. This error can be compensated/eliminated
by changing the image forming timing (scanning timing of the optical beam
21) so that image positions are shifted by Sm, Sc, and Sk which are
measured by a sensor such as a CCD camera.

SUMMARY

[0007]In a wet-developing image forming apparatuses using a liquid
developer obtained by dispersing toner particles in a high-viscosity
non-volatile carrier liquid, a carrier liquid on the intermediate
transfer belt is indispensable for secondary transfer of a toner image
onto a recording medium such as a paper in an image forming process.
However, a toner image containing the carrier liquid on the intermediate
transfer belt has high specularity, which may cause the resist marks to
erroneously be detected by a photo-detecting sensor. That is, at the
color shift compensation processing time in the image forming apparatus
disclosed in Patent Document 1, resist mark detection results obtained by
a sensor such as a CCD camera may degrade in accuracy, with the result
that accurate position information of the resist marks cannot be
obtained, thus preventing accurate color shift compensation.

[0008]In order to cope with this problem, a method can be considered in
which the carrier liquid on the intermediate transfer belt is removed at
the color shift compensation processing time. However, when the carrier
liquid on the intermediate transfer belt is removed, solid content ratio
in the resist marks is increased. When the resist marks on the
intermediate transfer belt proceed in the process downstream and pass
through a secondary transfer nip, the solid content ratio in the resist
marks is further increased. Then, there arises a new problem that
cleaning performance when cleaning the resist mark transferred onto the
intermediate transfer belt by means of a cleaning blade is deteriorated.

[0009]The present invention has been made to solve the above problem and,
according to a first aspect of the present invention, there is provided
an image forming apparatus including: a first image carrier; a first
charging section that charges the first image carrier; a first exposure
section that exposes the first image carrier charged by the first
charging section; a first developing section that develops a latent image
formed on the first image carrier in the first exposure section using a
first liquid developer containing a carrier and first toner particles; a
first primary transfer section that transfers a first image developed in
the first developing section onto a transfer medium; a second image
carrier; a second charging section that charges the second image carrier;
a second exposure section that exposes the second image carrier charged
by the second charging section; a second developing section that develops
a latent image formed on the second image carrier in the second exposure
section using a second liquid developer containing a carrier and second
toner particles; a second primary transfer section that transfers a
second image developed in the second developing section onto a transfer
medium; a carrier removal section of a transfer medium that removes the
carrier from the first and second images transferred on the transfer
medium; a condition storage section that stores a first condition in
which the carrier removal amount in the transfer medium carrier removal
section is set to a first carrier removal amount and a second condition
in which the carrier removal amount in the transfer medium carrier
removal section is set to a second carrier removal amount smaller than
the first carrier removal amount; an optical sensor that detects the
first and second images transferred on the transfer medium, from which
the carrier has been removed under the first condition stored in the
condition storage section; and a distance calculation section that
calculates the distance between the first and second images detected by
the optical sensor.

[0010]In the image forming apparatus according to the present invention,
the transfer medium carrier removal section is a roller, and the rotation
direction of the roller differs between the first and second conditions.

[0011]The image forming apparatus according to the present invention
further includes a second transfer medium carrier removal section that
removes a carrier from the first image transferred on the transfer
medium.

[0012]According to a second aspect of the present invention, there is
provided an image forming apparatus including: a first image carrier; a
first charging section that charges the first image carrier; a first
exposure section that exposes the first image carrier charged by the
first charging section; a first developing section that develops a latent
image formed on the first image carrier in the first exposure section
using a first liquid developer containing a carrier and first toner
particles; a first image carrier carrier removal section that removes the
carrier from a first image developed in the first developing section; a
first primary transfer section that transfers the first image from which
the carrier has been removed in the first image carrier carrier removal
section onto a transfer medium; a second image carrier; a second charging
section that charges the second image carrier; a second exposure section
that exposes the second image carrier charged by the second charging
section; a second developing section that develops a latent image formed
on the second image carrier in the second exposure section using a second
liquid developer containing the carrier and second toner particles; a
second image carrier carrier removal section that removes the carrier
from a second image developed in the second developing section; a second
primary transfer section that transfers the second image from which the
carrier has been removed in the second image carrier carrier removal
section onto a transfer medium; a condition storage section that stores a
first condition in which the carrier removal amount in the first image
carrier carrier removal section or second image carrier carrier removal
section is set to a first carrier removal amount and a second condition
in which the carrier removal amount in the first image carrier carrier
removal section or second image carrier carrier removal section is set to
a second carrier removal amount smaller than the first carrier removal
amount; an optical sensor that detects the first image transferred on the
transfer medium, from which the carrier has been removed in the first
image carrier carrier removal section under the first condition stored in
the condition storage section and second image transferred on the
transfer medium, from which the carrier has been removed in the second
image carrier carrier removal section under the first condition stored in
the condition storage section; and a distance calculation section that
calculates the distance between the first and second images detected by
the optical sensor.

[0013]In the image forming apparatus according to the present invention,
the first and second image carrier carrier removal sections are rollers,
and the rotation direction of the rollers differs between the first and
second conditions.

[0014]The image forming apparatus according to the present invention
further includes a carrier removal section of a transfer medium that
removes the carrier from the first and second images transferred on the
transfer medium.

[0015]The image forming apparatus according to the present invention
further includes a second transfer medium carrier removal section that
removes the carrier from the first image transferred on the transfer
medium.

[0016]The image forming apparatus according to the present invention
further includes a second first image carrier carrier removal section
that removes the carrier from the first image from which the carrier has
been removed in the first image carrier carrier removal section; and a
second second image carrier carrier removal section that removes the
carrier from the second image from which the carrier has been removed in
the second image carrier carrier removal section.

[0017]In the image forming apparatus according to the present invention,
the second first image carrier carrier removal section abuts and
separates thereon from the first image carrier, and the second second
image carrier carrier removal section abuts and separates thereon from
the second image carrier.

[0018]Further, according to a third aspect of the present invention, there
is provided an image forming apparatus control method, including:
charging a first image carrier by a first charging section; exposing the
first image carrier charged by the first charging section by a first
exposure section to form a latent image; developing the latent image
formed on the first image carrier in the first exposure section using a
first liquid developer containing a carrier and first toner particles by
a first developing section; removing the carrier from a first image
developed in the first developing section by a first image carrier
carrier removal section; transferring the first image from which the
carrier has been removed in the first image carrier carrier removal
section onto a transfer medium by a first primary transfer section;
charging a second image carrier by a second charging section; exposing
the second image carrier charged by the second charging section by a
second exposure section to form a latent image; developing the latent
image formed on the second image carrier in the second exposure section
using a second liquid developer containing the carrier and second toner
particles by a second developing section; removing the carrier from a
second image developed in the second developing section by a second image
carrier carrier removal section; transferring the second image from which
the carrier has been removed in the second image carrier carrier removal
section onto a transfer medium by a second primary transfer means; and
performing image formation on a first recording medium under a first
condition in which the carrier removal amount in the first image carrier
carrier removal section or second image carrier carrier removal section
is set to a first carrier removal amount, while performing image
formation on a second recording medium having a rougher surface than that
of the first recording medium under a second condition in which the
carrier removal amount in the first image carrier carrier removal section
or second image carrier carrier removal section is set to a second
carrier removal amount smaller than the first carrier removal amount.
When detecting the first and second images transferred on the transfer
member by an optical sensor and calculating the distance between the
first and second images detected by the optical sensor, the first
condition is used to perform image formation.

[0019]In the image forming apparatus control method according to the
present invention, the first and second image carrier carrier removal
sections are rollers, and the rotation direction of the rollers differs
between the first and second conditions.

[0020]The image forming apparatus control method according to the present
invention further includes removing the carrier from the first and second
images transferred on the transfer medium by a second transfer medium
carrier removal section.

[0021]The image forming apparatus control method according to the present
invention further including removing the carrier from the first image
transferred on the transfer medium by a second transfer medium carrier
removal section.

[0022]The image forming apparatus control method according to the present
invention further includes: removing the carrier from the first image
from which the carrier has been removed in the first image carrier
carrier removal section by a second first image carrier carrier removal
section; and removing the carrier from the second image from which the
carrier has been removed in the second image carrier carrier removal
section by a second second image carrier carrier removal section.

[0023]In the image forming apparatus control method according to the
present invention, the second first image carrier carrier removal section
abuts and separates thereon from the first image carrier, and the second
second image carrier carrier removal section abuts and separates thereon
from the second image carrier.

[0024]According to the present invention, when the color shift
compensation mode is executed, the removal amount of the carrier on the
intermediate transfer belt is increased as compared to the removal amount
in the normal printing operation, so that the position information of the
resist marks can be accurately acquired without deterioration in the
accuracy of the resist mark detection results obtained by the optical
sensor, thereby achieving accurate color shift compensation.

[0025]According to the present invention, when the carrier on the
intermediate transfer member is removed in order to prevent deterioration
in the accuracy of the resist mark detection results obtained by the
optical sensor in the color shift compensation mode, the color shift
compensation mode is executed under the same condition as in the image
forming mode in terms of the carrier removal amount. This prevents
deterioration in the cleaning performance when cleaning the resist marks
transferred onto the intermediate transfer member by means of the
intermediate transfer member cleaning blade.

[0026]The following reference embodiment is also possible. That is, an
image forming apparatus according to the present invention has: a
plurality of image carriers, for respective colors, that carry developed
images produced by using a liquid developer containing a carrier and
toner particles; an intermediate transfer member that moves in a
predetermined direction, onto which the developed images are transferred
from the plurality of image carriers; and an optical sensor that detects
the developed images transferred to predetermined positions on the
intermediate transfer member. The image forming apparatus has a color
shift compensation mode that transfers resist marks to predetermined
positions on the intermediate transfer member by the plurality of image
carriers, detects the resist marks by the optical sensor, calculates a
color shift amount between different colors, and compensates the
calculated color shift amount and a plurality of image forming modes
having different conditions concerning at least the removal amount of the
carrier on the intermediate transfer member. The color shift compensation
mode is executed under a condition of the same carrier removal amount as
in the image forming mode in which the removal amount of the carrier on
the intermediate transfer member is largest of all the image forming
modes provided in the image forming apparatus.

[0027]In the image forming apparatus according to the reference embodiment
of the present invention, the plurality of image forming modes are modes
that form images on different types of recording media.

[0028]The image forming apparatus according to the reference embodiment of
the present invention has an intermediate transfer member squeezing
roller arranged downstream relative to the plurality of image carriers
and changes the peripheral rotation speed of the intermediate transfer
member squeezing roller among the plurality of image forming modes to
change a condition concerning the removal amount of the carrier on the
intermediate transfer member.

[0029]The image forming apparatus according to the reference embodiment of
the present invention has a plurality of intermediate transfer member
squeezing rollers arranged respectively downstream relative to the
plurality of image carriers and changes the peripheral rotation speed of
the intermediate transfer member squeezing rollers among the plurality of
image forming modes to change a condition concerning the removal amount
of the carrier on the intermediate transfer member.

[0030]The image forming apparatus according to the reference embodiment of
the present invention has a plurality of image carrier squeezing rollers
abutting the plurality of image carriers respectively at the portions
upstream relative to the nips between the intermediate transfer member
and respective image carriers and changes the peripheral rotation speed
of the image carrier squeezing rollers among the plurality of image
forming modes to change a condition concerning the removal amount of the
carrier on the intermediate transfer member.

[0031]In the image forming apparatus according to the reference embodiment
of the present invention, the plurality of image forming modes are modes
in which toner consumption amount for use in an image forming process
differs from one another.

[0032]In the image forming apparatus according to the reference embodiment
of the present invention, the moving speed of the intermediate transfer
member is not changed among the plurality of image forming modes.

[0033]Further, an image forming apparatus control method according to the
reference embodiment of the present invention is a control method of an
image forming apparatus having: a plurality of image carriers, for
respective colors, that carry developed images produced by using a liquid
developer containing a carrier and toner particles; an intermediate
transfer member that moves in a predetermined direction, onto which the
developed images are transferred from the plurality of image carriers;
and an optical sensor that detects the developed images transferred to
predetermined positions on the intermediate transfer member. The image
forming apparatus control method includes a color shift compensation mode
that transfers resist marks to predetermined positions on the
intermediate transfer member by the plurality of image carriers, detects
the resist marks by the optical sensor, calculates a color shift amount
between different colors, and compensates the calculated color shift
amount and a plurality of image forming modes having different conditions
concerning at least the removal amount of the carrier on the intermediate
transfer member. The color shift compensation mode is executed under a
condition of the same carrier removal amount as in the image forming mode
in which the removal amount of the carrier on the intermediate transfer
member is largest of all the image forming modes provided in the image
forming apparatus.

[0034]According to the present invention, when the color shift
compensation mode is executed, the removal amount of the carrier on the
intermediate transfer belt is increased as compared to the removal amount
in the normal printing operation, so that the position information of the
resist marks can be accurately acquired without in the accuracy of
deterioration of the resist mark detection results obtained by the
optical sensor, thereby achieving accurate color shift compensation.

[0035]According to the present invention, when the carrier on the
intermediate transfer member is removed in order to prevent deterioration
in the accuracy of the resist mark detection results obtained by the
optical sensor in the color shift compensation mode, the color shift
compensation mode is executed under the same condition as in the image
forming mode in terms of the carrier removal amount. This prevents
deterioration in the cleaning performance when cleaning the resist marks
transferred onto the intermediate transfer member by means of the
intermediate transfer member cleaning blade.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a view showing main components constituting an image
forming apparatus according to a first embodiment of the present
invention;

[0037]FIG. 2 is a cross-sectional view showing main components of an image
forming section and developing unit in the first embodiment of the
present invention;

[0038]FIGS. 3A and 3B are views showing an intermediate transfer member
squeezing unit of the image forming apparatus according to embodiments of
the present invention;

[0039]FIG. 4 is a view showing main components constituting an image
forming apparatus according to a second embodiment of the present
invention;

[0040]FIG. 5 is a cross-sectional view showing main components of an image
forming section and developing unit in the second embodiment of the
present invention;

[0041]FIG. 6 is a view showing main components constituting an image
forming apparatus according to a fourth embodiment of the present
invention;

[0042]FIG. 7 is another view showing main components constituting an image
forming apparatus according to the fourth embodiment of the present
invention;

[0043]FIG. 8 is a cross-sectional view showing main components of an image
forming section and developing unit in the fourth embodiment of the
present invention;

[0044]FIGS. 9A and 9B are views showing main components of a developing
unit in the image forming apparatus according to a fifth embodiment of
the present invention;

[0045]FIGS. 10A and 10B are another views showing main components of the
developing unit in an image forming apparatus according to the fifth
embodiment of the present invention;

[0046]FIG. 11 is a view showing an example of resist marks formed onto an
intermediate transfer member 40;

[0050]FIG. 15 is a view showing a sensor output observed when resist marks
are detected by means of an optical sensor 90;

[0051]FIG. 16 is another view showing a sensor output observed when resist
marks are detected by means of an optical sensor 90; and

[0052]FIG. 17 is a view schematically showing a state where resist marks
are detected by means of an optical sensor 90.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053]Embodiments of the present invention will be described below with
reference to the accompanying drawings. FIG. 1 is a view showing main
components constituting an image forming apparatus according to a first
embodiment of the present invention. An image forming apparatus of this
embodiment has image forming sections of different colors that are
arranged at a middle part of the apparatus. Developing units 30Y, 30M,
30C and 30K are arranged in the lower part of the image forming apparatus
and intermediate transfer member 40 and a secondary transfer section
(secondary transfer unit) 60 are arranged in the upper part of the
apparatus.

[0054]The image forming sections are formed respectively by image carriers
10Y, 10M, 10C and 10K, corona chargers 11Y, 11M, 11C and 11K and not
shown exposure units 12Y, 12M, 12C and 12K. The exposure units 12Y, 12M
12C and 12K each have an optical system such as a semiconductor laser, a
polygon mirror, an F-θ lens. The image carriers 10Y, 10M, 10C and
10K are uniformly electrically charged by the respective corona chargers
11Y, 11M, 11C and 11K and exposed to respective beams of light that are
modulated respectively by input video signals by means of the exposure
units 12Y, 12M, 12C and 12K to form electrostatic latent images on the
electrically charged image carriers 10Y, 10M, 10C and 10K. The developing
units 30Y, 30M, 30C and 30K each have developing rollers 20Y, 20M, 20C
and 20K, developer reservoirs 31Y, 31M, 31C and 31K storing liquid
developer of different colors of yellow (Y), magenta (M), cyan (C) and
black (K), anilox rollers 32Y, 32M, 32C and 32K which are application
rollers for applying the liquid developer of these colors from the
developer reservoirs 31Y, 31M, 31C and 31K to the developing rollers 20Y,
20M, 20C and 20K, and the like and develop the electrostatic latent
images formed on the image carriers 10Y, 10M, 10C and 10K by means of the
liquid developer of the different colors.

[0055]The intermediate transfer member 40 is an endless belt that is wound
around a drive roller 41 and a tension roller 42 and is driven to rotate
by the drive roller 41, while it is brought into abutting the image
carriers 10Y, 10M, 10C and 10K respectively at primary transfer sections
50Y, 50M, 50C and 50K. In the primary transfer sections 50Y, 50M, 50C and
50K, the image carriers 10Y, 10M, 10C and 10K are respectively arranged
opposite to primary transfer rollers 51Y, 51M, 51C and 51K with the
intermediate transfer member 40 interposed between them. The toner images
of the different colors on the image carriers 10Y, 10M, 10C and 10K are
sequentially transferred onto the intermediate transfer member 40 one on
the other at the respective transfer positions that are the abutting
positions between the intermediate transfer member 40 and the image
carriers 10Y, 10M, 10C and 10K so as to form a full color toner image.

[0056]In the secondary transfer unit 60, a secondary transfer roller 61 is
arranged opposite to a belt drive roller 41 with the intermediate
transfer member 40 interposed between them. Further, a cleaning unit that
includes a secondary transfer roller cleaning blade 62 is also arranged
in the secondary transfer unit 60. At the transfer position at which the
secondary roller 61 is provided, a single color toner image or full color
toner image formed on the intermediate transfer member 40 is transferred
onto a recording medium such as a paper, a film or a cloth conveyed along
a sheet member conveyance route L.

[0057]A fixing unit 90 is arranged on the downstream side of the sheet
member conveyance route L. The fixing unit 90 fixes the single color
toner image or the full color toner image transferred onto the recording
medium such as a paper by fusion.

[0058]The tension roller 42 supports the intermediate transfer member 40
together with the belt drive roller 41. A cleaning unit including an
intermediate transfer member cleaning blade 46 is so arranged as to be
brought into abutting the tension roller 42 at the location where the
intermediate transfer member 40 is wound around the tension roller 42.

[0059]Now, the image forming sections and developing units will be
described below. FIG. 2 is a cross-sectional view showing main components
of the image forming section and developing unit in the first embodiment
of the present invention. Since the image forming sections and developing
units of different colors respectively have the same configuration, the
image forming section and the developing unit of Y (yellow) will be
described below.

[0060]In the image forming section, an image carrier cleaning roller 16Y,
an image carrier cleaning blade 18Y, a corona charger 11Y, an exposure
unit 12Y, a developing roller 20Y of the developing unit 30Y and an image
carrier squeezing roller 13Y are arranged along the outer periphery of
the image carrier 10Y in the mentioned order as viewed in the sense of
rotation thereof.

[0062]Reference numeral 70Y denotes a first image carrier developer
collection section for receiving a liquid developer dropped from the
image carrier squeezing roller cleaning blade 14Y, and reference numeral
73Y is a third image carrier developer collection section for receiving a
liquid developer dropped from the image carrier cleaning roller cleaning
blade 17Y and image carrier cleaning blade 18Y. A pipe for evacuating the
liquid developer received from the blade is connected to the lower part
of the first image carrier developer collection section 70Y. Similarly, a
pipe for evacuating the liquid developer received from the blade is
connected to the lower part of the third image carrier developer
collection section 73Y.

[0063]A developing roller cleaning blade 21Y, an anilox roller 32Y, and a
toner compression corona generator 22Y are arranged along the outer
periphery of the developing roller 20Y in the developing unit 30Y. A
restricting blade 33Y for controlling the amount of a liquid developer
supplied to the developing roller 20Y is brought into abutting the anilox
roller 32Y.

[0064]A reference numeral 72Y denotes a developing roller developer
collection section for receiving a liquid developer dropped from the
developing roller cleaning blade 21Y. A pipe for evacuating the liquid
developer received from the blade is connected to the lower part of the
developing roller developer collection section 72Y. A liquid developer
supply roller 34Y is housed in the developer reservoir 31Y.

[0065]The primary transfer roller 51Y of the primary transfer section is
arranged at the position opposite to the image carrier 10Y along the
intermediate transfer member 40.

[0066]FIGS. 3A and 3B are views showing an intermediate transfer member
squeezing unit of the image forming apparatus according to embodiments of
the present invention. The intermediate transfer member squeezing unit is
configured to squeeze the intermediate transfer member 40 at the portion
immediately downstream relative to the transfer nip of the image carrier
10K. In the present embodiment, an intermediate transfer member squeezing
unit 52K including an intermediate transfer member squeezing roller 53K,
a backup roller 54K, and an intermediate transfer member squeezing roller
cleaning blade 55K is arranged along the intermediate transfer member 40
at the portion downstream side relative to the developing unit 30K in the
moving direction of the intermediate transfer member 40.

[0067]Reference numeral 84K is a first intermediate transfer member
developer collection section for receiving a liquid developer dropped
from the intermediate transfer member squeezing roller cleaning blade
55K. A pipe for evacuating the liquid developer received from the blade
is connected to the lower part of the first intermediate transfer member
developer collection section 84K.

[0068]The image carrier 10Y is a photosensitive drum that is a cylindrical
member having a width broader than the width of the developing roller 20Y
and having a photosensitive layer formed on the outer peripheral surface
thereof. The image carrier 10Y rotates clockwise as shown in FIG. 2. The
photosensitive layer of the image carrier 10Y is typically formed by
using an organic image carrier or an amorphous silicon image carrier. The
corona charger 11Y is arranged at the upstream side relative to the nip
portion formed between the image carrier 10Y and the developing roller
20Y in the sense of rotation of the image carrier 10Y. A voltage is
applied from a power source (not shown) to corona charge the image
carrier 10Y. The exposure unit 12Y is arranged at the downstream side
relative to the corona charger 11Y in the sense of rotation of the image
carrier 10Y to expose the electrically charged surface of the image
carrier 10Y to a laser light and form a latent image on the image carrier
10Y.

[0069]The components such as rollers arranged in the earlier stage in the
image forming process are assumed to be located on the upstream relative
to components such as rollers arranged in the later stage thereof.

[0070]The developing unit 30Y includes the toner compression corona
generator 22Y for exerting a compaction effect and developer reservoir
31Y storing a liquid developer in which toner is dispersed in carrier
liquid to a weight ratio of about 20%.

[0071]Further, as described above, the developing unit 30Y includes the
development roller 20Y bearing the liquid developer, anilox roller 32Y
that functions as an application roller for applying the liquid developer
to the developing roller 20Y, restricting blade 33Y for resting the
amount of the liquid developer to be applied to the developing roller
20Y, supply roller 34 for supplying the liquid developer to the anilox
roller 32Y while agitating and conveying the liquid developer, toner
compression corona generator 22Y for making the liquid developer borne on
the developing roller 20Y in a compacted state, and developing roller
cleaning blade 21Y for cleaning the developing roller 20Y.

[0072]The liquid developer contained in the developer container 31Y is not
a popular volatile low concentration (about 1 to 2 wt %) and low
viscosity liquid developer that is volatile at room temperature and
prepared by using Isopar (trademark, available from Exxon) as carrier
liquid but a non-volatile high concentration and high viscosity liquid
developer that is not volatile at room temperature. More specifically,
the liquid developer that is employed for the purpose of the present
invention is a high viscosity (about 30 to 10,000 mPas) liquid developer
prepared by adding solid particles of an average particle size of 1
μm, which are formed by dispersing a coloring agent such as a pigment
in thermoplastic resin, in a liquid solvent such as an organic solvent,
silicon oil, mineral oil or edible oil with a dispersing agent to make
the toner solid concentration equal to about 20%.

[0073]The anilox roller 32Y functions as an application roller for
supplying the liquid developer to the developing roller 20Y and applying
the liquid developer to the same. The anilox roller 32Y is a cylindrical
roller having an undulated surface produced by uniformly forming fine
helical grooves so as to make it easily bear a liquid developer. The
liquid developer is supplied from the developer reservoir 31Y to the
developing roller 20Y by means of the anilox roller 32Y. As shown in FIG.
2, when the apparatus is running, the supply roller 34Y rotates clockwise
to supply the liquid developer to the anilox roller 32Y, and the anilox
roller 32Y rotates counterclockwise to apply the liquid developer to the
developing roller 20Y.

[0074]The restricting blade 33Y is an elastic blade having an elastic
member arranged on the surface thereof. More specifically, the
restricting blade 33Y includes a rubber section that is typically made of
urethan rubber and is brought into abutting the surface of the anilox
roller 32Y and a metal plate supporting the rubber section. The
restricting blade 33Y restricts and adjusts the film thickness and the
amount of the liquid developer conveyed by the anilox roller 32Y, and
also adjusts the amount of the liquid developer to be supplied to the
developing roller 20Y.

[0075]The developing roller 20Y is a cylindrical member that is driven to
rotate counterclockwise around the axis of rotation thereof as shown in
FIG. 2. The developing roller 20Y is formed by arranging an elastic layer
typically made of polyurethane rubber, silicon rubber or NBR on the outer
peripheral surface of an inner core, which is typically made of iron or
some other metal. The developing roller cleaning blade 21Y is typically
made of rubber and brought into abutting the surface of the developing
roller 20Y. The developing roller cleaning blade 21Y is arranged at the
downstream side relative to the development nip where the developing
roller 20Y is brought into abutting the image carrier 10Y in the sense of
rotation of the developing roller 20Y so as to scrape off and remove the
liquid developer remaining on the developing roller 20Y.

[0076]The toner compression corona generator 22Y is an electric field
application means for increasing a charged bias on the surface of the
developing roller 20Y. The liquid developer conveyed by the developing
roller 20Y is subjected to the application of an electric field by the
toner compression corona generator 22Y at toner compression site in the
direction from the toner compression corona generator 22Y toward the
developing roller 20Y, as shown in FIG. 2.

[0077]As the electric field application means for toner compression, a
compaction roller may be used in place of the corona discharger shown in
FIG. 2 producing corona discharge. Such a compaction roller may be a
cylindrical member and formed as an elastic roller by covering the
surface thereof with an elastic material like the developing roller 20 Y.
More specifically, the compaction roller may have a structure provided
with a conductive resin layer or rubber layer is on an surface layer of a
metal roller base material, and rotate in the clockwise direction
opposite to the rotation direction of the developing roller 20Y.

[0078]The developer carried and toner-compressed by the developing roller
20Y is applied with an electric field at the development nip where the
developing roller 20Y is brought into abutting the image carrier 10Y so
as to be developed according to the latent image on the image carrier
10Y. The residual developer remaining on the development roller 20Y is
scraped off and removed by the developing roller cleaning blade 21Y and
dropped to the developing roller developer collection section 72Y so as
to be reused. Note that the carrier liquid and the toner dropped to the
developing roller developer collection section 72Y are not in a mixed
color state.

[0079]An image carrier squeezing unit on the upstream side relative to the
primary transfer is located on the downstream side relative to the
developing device 20Y, opposed to the image carrier member 10Y, and
collects the residual developer that is produced after the toner image on
the image carrier 10Y is developed. The image carrier squeezing unit
includes the image carrier squeezing roller 13Y constituted by an elastic
roller member which has a surface covered with an elastic member and is
brought into sliding contact with the image carrier 10Y so as to be
driven to rotate and image carrier squeezing roller cleaning blade 14Y
pressed against and brought into sliding contact with the image carrier
squeezing roller 13Y to clean the surface thereof. The image carrier
squeezing unit has a function of collecting the surplus carrier liquid
and the unnecessary fogging toner from the developer of the image
developed on the image carrier 10Y to raise the toner particle content
ratio in the developed visible image.

[0080]In the primary transfer section 50Y, the developer image developed
on the image carrier 10Y is transferred onto the intermediate transfer
member 40 by the primary transfer roller 51Y. In this process, the image
carrier 10Y and the intermediate transfer member 40 are configured to
move at an equal speed, so that load caused by rotation and motion
thereof is reduced and disturbance on the visualized toner image on the
image carrier 10Y is suppressed.

[0081]A cleaning unit on the downstream side of the primary transfer is
located on the downstream side relative to the primary transfer section
50Y, opposed to the image carrier member 10Y, and collects the residual
liquid developer on the image carrier member 10Y before an electrostatic
latent image is formed. The cleaning unit includes, as shown in FIG. 2,
the image carrier cleaning roller 16Y constituted by an elastic roller
member which has a surface covered with an elastic member and is brought
into sliding contact with the image carrier 10Y so as to be driven to
rotate and image carrier cleaning roller cleaning blade 17Y pressed
against and brought into sliding contact with the image carrier squeezing
roller 16Y to clean the surface thereof. The cleaning unit has a function
of collecting the surplus carrier liquid and the unnecessary toner that
has not been transferred. The image carrier cleaning roller 16Y has a
structure in which a rubber layer is arranged on the surface of a metal
roller base material and is applied with a bias voltage that attracts
toner particles on the image carrier 11. The image carrier cleaning
roller 16Y is provided mainly for the purpose of cleaning a toner
particle component contained in the residual liquid developer.

[0082]The image carrier cleaning blade 18Y configured to perfectly clean
the surface of the image carrier 10Y before a new electrostatic latent
image is formed is arranged on the downstream side relative to the image
carrier cleaning roller 16Y. The image carrier cleaning blade 18Y is
provided mainly for the purpose of cleaning a carrier component contained
in the residual liquid developer.

[0083]The intermediate transfer member squeezing unit 52K is arranged at
the downstream side relative to the primary transfer section 50K to
remove the surplus carrier liquid on the intermediate transfer member 40
and raise the toner particle content ratio in the developed visible
image. In practicing the present invention, such a squeezing unit may be
arranged at an arbitrary location upstream relative to a detection
section of an optical sensor 90.

[0084]Like the image carrier squeezing units, the intermediate transfer
member squeezing unit 52K includes an intermediate transfer member
squeezing roller 53K which is an elastic roller member having an elastic
member arranged on the surface thereof and brought into sliding contact
with the intermediate transfer member 40 so as to be driven to rotate, a
backup roller 54K arranged opposite to the intermediate transfer member
squeezing roller 53K with the intermediate transfer member 40 interposed
between them, a cleaning blade 55K pressed against and brought into
sliding contact with intermediate transfer member squeezing roller 53K to
collect the surplus carrier and unnecessary fogging toner from the
developer primary-transferred onto the intermediate transfer member 40.

[0085]Next, the flow of the liquid developer in the image forming
apparatus according to the present invention will be described with
reference to FIGS. 1 and 2. The secondary transfer roller 61 is arranged
opposite to the belt drive roller 41 with the intermediate transfer
member 40 interposed between them. Further, the cleaning unit including
the secondary transfer roller cleaning blade 62 is also arranged for the
secondary transfer roller 61.

[0086]Reference numeral 63 is a secondary transfer roller developer
collection section for receiving the liquid developer dropped from the
secondary roller cleaning blade 62. A pipe for evacuating the liquid
developer received from the blade is connected to the lower part of the
secondary transfer roller developer collection section 63. This pipe
communicates with a first waste tank 440. The liquid developer scraped
off by the secondary transfer roller cleaning blade 62 is a liquid
developer in which toners of different colors are mixed, so that the
liquid developer collected in the secondary transfer roller developer
collection section 63 is discharged to the first waste tank 440 through
the pipe.

[0087]Reference numeral 47 is a secondary intermediate transfer member
developer collection section for receiving the liquid developer dropped
from the intermediate transfer member cleaning blade 46. A pipe for
evacuating the liquid developer received from the blade is connected to
the lower part of the secondary intermediate transfer member developer
collection section 47. This pipe communicates with a second waste tank
441. The liquid developer scraped off by the intermediate transfer member
cleaning blade 46 is a liquid developer in which toners of different
colors are mixed, so that the liquid developer collected in the secondary
intermediate transfer member developer collection section 47 is
discharged to the second waste tank 440 through the pipe.

[0089]The agitation tanks 400Y, 400M, 400C, and 400K are tanks for
preparing a liquid developer having a toner solid concentration of about
20% to be supplied to the developer reservoirs 31Y, 31M, 31C, and 31K.

[0090]The developer supply tanks 401Y, 401M, 401C, and 401K are tanks for
storing a high concentration toner having a toner solid concentration of
20% or more. The carrier tank 410, which is a tank for storing a carrier
stock solution, is piped to the agitation tanks 400Y, 400M, 400C, and
400K of respective colors through the fourth pumps 453Y, 453M, 453C, and
453K.

[0091]The agitation tanks 400Y, 400M, 400C, and 400K receive supply of
high concentration toners from the developer supply tanks 401Y, 401M,
401C, and 401K. To this end, the second pumps 451Y, 451M, 451C, and 451K
are driven.

[0092]The agitation tanks 400Y, 400M, 400C, and 400K also receive supply
of a carrier stock solution from the carrier tank 410 by means of the
drive of the fourth pumps 453Y, 453M, 453C, and 453K.

[0093]The agitation tanks 400Y, 400M, 400C, and 400K are each provided
with toner concentration detection means (not shown) such as an optical
sensor. The agitation tanks 400Y, 400M, 400C, and 400K use the toner
concentration detection means to detect the concentration and perform
on/off control of the respective pumps using a not shown controller so as
to maintain appropriate concentration of the liquid developer in the
agitation tanks 400Y, 400M, 400C, and 400K. Further, the agitation tanks
400Y, 400M, 400C, and 400K are each provided with not shown agitation
units and uniformly agitate the developer therein by driving the
agitation units.

[0094]During the operating time of the apparatus, adequate amount of
liquid developer is always supplied from the agitation tanks 400Y, 400M,
400C, and 400K to the developer reservoirs 31Y, 31M, 31C, and 31K by
means of the first pumps 450Y, 450M, 450C, and 450K.

[0095]The liquid developer collected in the first image carrier developer
collection sections 70Y, 70M, 70C, and 70K and developing roller
developer collection section 72Y, 72M, 72C, and 72K is introduced into
the agitation tanks 400Y, 400M, 400C, and 400K through the pipes so as to
be reused.

[0096]The liquid developer collected in the third image carrier developer
collection sections 73Y, 73M, 73C, and 73K is introduced into the buffer
tanks 402Y, 402M, 402C, and 402K through the pipes for temporary storage.
The liquid developer in the buffer tanks 402Y, 402M, 402C, and 402K is
fed to the agitation tanks 400Y, 400M, 400C, and 400K by the operation of
the second pumps 451Y, 451M, 451C, and 451K. The reason that the second
pumps 451Y, 451M, 451C, and 451K are used here is that the solid
concentration of the liquid developer collected in the third image
carrier developer collection sections 73Y, 73M, 73C, and 73K is high.

[0097]The liquid developer collected in the developer collection sections
of respective color units has not been subjected to color superposition
and therefore are not in a mixed color state, so that it is to be reused.
On the other hand, the liquid developer collected in the first
intermediate transfer member developer collection section 84K is a liquid
developer in which toners of different colors are mixed, so that the
liquid developer collected in the first intermediate transfer member
developer collection section 84K is discharged to the second waste tank
441 through the pipe.

[0098]Next, a determination means for realizing a plurality of modes in
which images are formed in different types of recording media will be
described. The image forming apparatus according to the present invention
has a plurality of image forming modes by which images can be printed on
different types of papers (art paper, coated paper, high-quality paper,
regular paper, etc.).

[0099]The reason that the plurality of image forming modes corresponding
to the paper types are required is that the amount of the carrier
required in an image forming process differs depending on the paper type.
The image forming apparatus according to the present invention has two
image forming modes for a first type recording medium, typified by art
paper, coated paper, etc., having a comparatively smooth surface on which
there is little unevenness as viewed microscopically and a second type
recording medium, typified by high-quality paper, regular paper, etc.,
having a comparatively rough surface on which there is much unevenness as
viewed microscopically.

[0100]In order to achieve a transfer process including primary and
secondary transfer using a liquid developer, a sufficient amount of a
carrier is required to electrophorese the toner. Therefore, the amount of
a carrier required for the first type recording medium having a surface
on which there is little unevenness is small, and amount of a carrier
required for the second type recording medium having a surface on which
there is much unevenness is larger than the case of the first type
recording medium.

[0101]In the present embodiment, a paper type determination sensor 5 as
shown in FIG. 1 is provided for detecting the type of a recording medium.
The paper type determination sensor 5 is constituted by a light-emitting
element 6 that irradiates a recording medium conveyed along the
conveyance route with a light and a light receiving element 7 that
detects reflection of the reflected light from the recording medium. In
the present embodiment, a signal such as reflectance of the reflected
light is input from the light-receiving element 7 to a not shown
controller such as a CPU, where the type (art paper, coated paper,
high-quality paper, regular paper, etc.) of the recording medium is
determined.

[0102]Next, a color shift compensation mode in the present invention will
be described. There exists a problem of color shift in the image forming
apparatus according to the present invention that performs image
formation using developing units 30Y, 30M, 30C, and 30K of four colors.
That is, when toner images respectively formed by the different
developing units 30Y, 30M, 30C, and 30K are transferred onto the
intermediate transfer member 40, the transfer positions are shifted from
one another, which appears as a change in the color tone on a recording
medium.

[0103]To eliminate this problem, the image formation apparatus has a color
shift compensation mode. In this color shift compensation mode, reference
pattern images (hereinafter, referred to as "resist marks") for detecting
color shift, which are previously formed on the intermediate transfer
member 40, are detected using the optical sensor 90 to acquire position
information of the resist marks, and positioning (color shift
compensation processing, displacement compensation processing) of
respective toner images are performed based on the acquired position
information.

[0104]The optical sensor 90 for detecting the resist marks are provided at
the preceding stage of the transfer nip of the secondary transfer unit 60
as shown in FIG. 1. As the optical sensor 90, a known device such as a
light-emitting and light-receiving element pair or CCD camera can be
used.

[0106]The resist marks thus formed are detected by the optical sensor 90,
and color shift amount between different colors is calculated by a not
shown calculation means. In the color shift compensation mode, the image
forming apparatus is controlled such that the color shift amount
calculated by the calculation means is compensated by a known means.

[0107]A toner image containing the carrier liquid on the intermediate
transfer member 40 has high specularity, which may cause the resist marks
to erroneously be detected by the optical sensor 90. That is, at the
color shift compensation processing time in a wet-developing image
forming apparatus, resist mark detection results obtained by the optical
sensor 90 may degrade in accuracy, with the result that accurate position
information of the resist marks cannot be obtained, thus preventing
accurate color shift compensation.

[0108]In order to cope with this problem, a method can be considered in
which the carrier liquid on the intermediate transfer member 40 is
removed at the color shift compensation processing time. However, when
the carrier liquid on the intermediate transfer member 40 is removed,
solid content ratio in the resist marks is increased. When the resist
marks on the intermediate transfer member 40 proceed in the process
downstream and pass through the secondary transfer unit 60, the solid
content ratio in the resist marks are further increased. Then, there
arises a new problem that cleaning performance when cleaning the resist
marks transferred onto the intermediate transfer member 40 by means of
the intermediate transfer member cleaning blade 46 is deteriorated.

[0109]In view of this, at execution time of the color shift compensation
mode in the present invention, the carrier contained in the resist marks
is removed while the removal amount thereof is controlled so as not to be
excessive. More specifically, the color shift compensation mode in the
present invention is executed under a condition of the same carrier
removal amount as in the image forming mode in which the removal amount
of the carrier on the intermediate transfer member 40 is largest of all
the image forming modes provided in the image forming apparatus.

[0110]Thus, as described above, when the carrier on the intermediate
transfer member 40 is removed in order to prevent deterioration in the
accuracy of the resist mark detection results obtained by the optical
sensor 90 in the color shift compensation mode, the color shift
compensation mode is executed under the same condition as in the image
forming mode in terms of the carrier removal amount. This prevents
deterioration in the cleaning performance when cleaning the resist marks
transferred onto the intermediate transfer member 40 by means of the
intermediate transfer member cleaning blade. That is, according to the
present invention, there can be provided an image forming apparatus
capable of achieving both the prevention of deterioration in the resist
mark detection accuracy and prevention of deterioration in the cleaning
performance with respect to the intermediate transfer member in a
balanced manner.

[0111]An example of a plurality of image forming modes provided in an
image forming apparatus includes those by which images can be formed on
different types of papers. The image forming apparatus according to the
present invention has two image forming modes: a mode (first type
recording medium image forming mode) for image forming on a first type
recording medium (art paper and coated paper) having a surface on which
there is comparatively little unevenness and a mode (second type
recording medium image forming mode) for image forming on a second type
recording medium (high-quality paper and regular paper) having a surface
on which there is comparatively much unevenness. The amount of a carrier
required in the first type recording medium image forming mode is
controlled to be small, and amount of a carrier required in the second
type recording medium image forming mode is controlled to be larger than
the first type recording medium image forming mode. In the first
embodiment, the color shift compensation mode is executed under a
condition (first condition) of the same carrier removal amount as in the
first type recording medium image forming mode.

[0112]When the second type recording medium image forming mode is
executed, the intermediate transfer member squeezing roller 53K of the
intermediate transfer member squeezing unit is controlled to be rotated
at the same peripheral rotation speed as the moving speed of the
intermediate transfer member 40. On the other hand, in the first type
recording medium forming mode, the intermediate transfer member squeezing
roller 53K is controlled to be rotated at a peripheral rotation speed
higher than the moving speed of the intermediate transfer member 40 to
increase the amount of the carrier on the intermediate transfer member 40
to be removed by the intermediate transfer member squeezing roller 53K as
compared to the removal amount in the second type recording medium image
forming mode so as to achieve an optimum condition for image forming on a
recording medium such as art paper or coated paper. In the present
embodiment, the same carrier removal condition (this carrier removal
condition is referred to as "first condition") as in this first type
recording medium image forming mode is applied to the color shift
compensation mode (note that the carrier removal condition in the second
type recording medium image forming mode is referred to as "second
condition").

[0113]An example of conditions at the execution time of the first and
second type recording medium image forming modes in the first embodiment
of the present invention is shown in the following Table 1.

[0114]Another example of the operation of the intermediate transfer member
squeezing unit will be described below. FIG. 3A shows a state of the
intermediate transfer member squeezing unit at the execution time of the
second type recording medium image forming mode, and FIG. 3B shows a
state of the intermediate transfer member squeezing unit at the execution
time of the first type recording medium image forming mode. As shown in
FIGS. 3A and 3B, a configuration may be adopted in which, in the second
type recording medium image forming mode, the intermediate transfer
member squeezing roller 53K is controlled to be rotated in the same
direction as the moving direction of the intermediate transfer member 40
at the nip portion, while in the first type recording medium image
forming mode, the intermediate transfer member squeezing roller 53K is
controlled to be rotated in the reverse direction to the moving direction
of the intermediate transfer member 40 at the nip portion so as to
increase the amount of the carrier on the intermediate transfer member 40
to be removed by the intermediate transfer member squeezing roller 53K as
compared to the removal amount in the second type recording medium image
forming mode. In the present embodiment, the same carrier removal
condition as in such a first type recording medium image forming mode may
be applied to the color shift compensation mode.

[0115]The conditions for the operation of the squeezing unit and other
components at the execution time of the first type recording medium image
forming mode, second type recording medium image forming mode, and color
shift compensation mode are stored in a not shown storage means, and when
each of the above modes is executed, a corresponding condition stored in
the storage means is applied. Such a configuration is applied to all
embodiments of the present invention.

[0116]Further, in the first type recording medium image forming mode, the
intermediate transfer member squeezing roller 53K may be controlled to be
rotated at a peripheral rotation speed higher than the moving speed of
the intermediate transfer member 40 in the reverse direction to the
moving direction of the intermediate transfer member 40 at the nip
portion. The same carrier removal condition as in such a first type
recording medium image forming mode may be applied to the color shift
compensation mode.

[0117]In the example shown in FIG. 3B, the intermediate transfer member
squeezing roller 53K is rotated in the reverse direction to the moving
direction of the intermediate transfer member 40, so that the resist
marks formed on the intermediate transfer member 40 may be disturbed.
Thus, in the color shift compensation mode, a bias voltage for pressing
the toner in the resist marks from the intermediate transfer member
squeezing roller 53K to the intermediate transfer member 40 is preferably
applied.

[0118]As described above, according to the first embodiment of the present
invention, since the color shift compensation mode is executed under the
same condition as in the first type recording medium image forming mode
in which the removal amount of the carrier on the intermediate transfer
member 40 is increased as compared to the removal amount in the second
type recording medium image forming mode, the position information of the
resist marks can be accurately acquired without deterioration in the
accuracy of the resist mark detection results obtained by the optical
sensor, thereby achieving accurate color shift compensation. Further,
since the color shift compensation mode is executed under the same
condition as in the image forming mode provided in the image forming
apparatus in terms of the removal amount of the carrier on the
intermediate transfer member 40, it is possible to prevent deterioration
in the cleaning performance of the cleaning blade for cleaning the resist
marks transferred onto the intermediate transfer medium 40. That is,
according to the present invention, there can be provided an image
forming apparatus capable of achieving both the prevention of
deterioration in the resist mark detection accuracy and prevention of
deterioration in the cleaning performance with respect to the
intermediate transfer member in a balanced manner.

[0119]Next, a second embodiment of the present invention will be
described. FIG. 4 is a view showing main components constituting an image
forming apparatus according to the second embodiment of the present
invention, and FIG. 5 is a cross-sectional view showing main components
of an image forming section and developing unit in the second embodiment
of the present invention.

[0120]In the first embodiment, the intermediate transfer member squeezing
unit is provided only at the portion immediately downstream relative to
the transfer nip of the image carrier 10K, while in the second
embodiment, four intermediate transfer member squeezing units are
provided at the portions immediately downstream relative to respective
transfer nips of the image carriers 10Y, 10M, 10C, and 10K.

[0121]With reference to FIG. 5, the intermediate transfer member squeezing
units will be described by taking the intermediate transfer member
squeezing unit provided at the portion immediately downstream relative to
the transfer nip of the image carrier 10Y as an example. Since the
intermediate transfer member squeezing units provided for the developing
units of other colors have the same configuration, only the intermediate
transfer member squeezing unit provided for the developing unit of yellow
will be described below.

[0122]The intermediate transfer member squeezing unit (in this case, for
developing unit of yellow color) according to the second embodiment
squeezes the intermediate transfer member 40 at the portion immediately
downstream relative to the transfer nip of the image carrier 10Y. In the
present embodiment, an intermediate transfer member squeezing unit 52Y
constituted by an intermediate transfer member squeezing roller 53Y, a
backup roller 54Y, an intermediate transfer member squeezing roller
cleaning blade 55Y is arranged on the downstream side relative to the
developing unit 30Y in the moving direction of the intermediate transfer
member 40.

[0123]Reference numeral 84Y is a first intermediate transfer member
developer collection section for receiving a liquid developer dropped
from the intermediate transfer member squeezing roller cleaning blade
55Y. A pipe for evacuating the liquid developer received from the blade
is connected to the lower part of the first intermediate transfer member
developer collection section 84Y. The liquid developer collected in the
first intermediate transfer member developer collection section 84Y is a
liquid developer in which toners of different colors are mixed, so that
the liquid developer collected in first intermediate transfer member
developer collection section 84Y is discharged to the second waste tank
441 through the pipe and is not reused.

[0124]In the second embodiment, the intermediate transfer member squeezing
units 52Y, 52M, 52C, and 52K are used to switch the carrier removal
condition between the first and second type recording medium image
forming modes.

[0125]Also in the second embodiment, the color shift compensation mode is
executed under the condition in which the removal amount of the carrier
on the intermediate transfer member 40 is increased as compared to the
removal amount in the second type recording medium image forming mode. As
the concrete condition in this case, the same condition set in the first
type recording medium image forming mode is adopted.

[0126]In the image forming apparatus according to the second embodiment of
the present invention, when executing the color shift compensation mode,
the intermediate transfer member squeezing units 52Y, 52M, 52C, and 52K
provided immediately downstream relative to the primary transfer nips of
the image carriers of respective colors are used to remove a larger
amount of carrier than in the second type recording medium image forming
mode. In the present embodiment, the same carrier removal condition as in
this first type recording medium forming mode is applied to the color
shift compensation mode.

[0127]When the second type recording medium image forming mode is
executed, the intermediate transfer member squeezing rollers 53Y, 53M,
53C, and 53K of the intermediate transfer member squeezing units 52Y,
52M, 52C, and 52K are controlled to be rotated at the same peripheral
rotation speed as the moving speed of the intermediate transfer member
40. On the other hand, in the first type recording medium forming mode,
the intermediate transfer member squeezing rollers 53Y, 53M, 53C, and 53K
are controlled to be rotated at a peripheral rotation speed higher than
the moving speed of the intermediate transfer member 40 to increase the
amount of the carrier on the intermediate transfer member 40 to be
removed by the intermediate transfer member squeezing rollers 53Y, 53M,
53C, and 53K as compared to the removal amount in the second type
recording medium image forming mode. The same carrier removal condition
as in this first type recording medium image forming mode is applied to
the color shift compensation mode.

[0128]An example of conditions at the execution time of the first and
second type recording medium image forming modes in the second embodiment
is shown in the following Table 2.

[0129]Although not shown, a configuration may be adopted in which, in the
second type recording medium image forming mode, the intermediate
transfer member squeezing rollers 53Y, 53M, 53C, and 53K are controlled
to be rotated in the same direction as the moving direction of the
intermediate transfer member 40 at the respective nip portions, while in
the first type recording medium image forming mode, the intermediate
transfer member squeezing rollers 53Y, 53M, 53C, and 53K are controlled
to be rotated in the reverse direction to the moving direction of the
intermediate transfer member 40 at the respective nip portions so as to
increase the amount of the carrier on the intermediate transfer member 40
to be removed by the intermediate transfer member squeezing rollers 53Y,
53M, 53C, and 53K as compared to the removal amount in the second type
recording medium image forming mode. The same carrier removal condition
as in such a first type recording medium image forming mode may be
applied to the color shift compensation mode.

[0130]Further, in the first type recording medium image forming mode, the
intermediate transfer member squeezing rollers 53Y, 53M, 53C, and 53K may
be controlled to be rotated at a peripheral rotation speed higher than
the moving speed of the intermediate transfer member 40 in the reverse
direction to the moving direction of the intermediate transfer member 40
at the respective nip portions. The same carrier removal condition as in
such a first type recording medium image forming mode may be applied to
the color shift compensation mode.

[0131]In the above cases, the intermediate transfer member squeezing
rollers 53Y, 53M, 53C, and 53K are rotated in the reverse direction to
the moving direction of the intermediate transfer member 40, so that the
resist marks formed on the intermediate transfer member 40 may be
disturbed. Thus, in the color shift compensation mode, a bias voltage for
pressing the toner in the resist marks from the intermediate transfer
member squeezing rollers 53Y, 53M, 53C, and 53K to the intermediate
transfer member 40 is preferably applied.

[0132]As described above, according to the second embodiment of the
present invention, since the color shift compensation mode is executed
under the same condition as in the first type recording medium image
forming mode in which the removal amount of the carrier on the
intermediate transfer member 40 is increased as compared to the removal
amount in the second type recording medium image forming mode, the
position information of the resist marks can be accurately acquired
without deterioration in the accuracy of the resist mark detection
results obtained by the optical sensor, thereby achieving accurate color
shift compensation. Further, since the color shift compensation mode is
executed under the same condition as in the image forming mode provided
in the image forming apparatus in terms of the removal amount of the
carrier on the intermediate transfer member 40, it is possible to prevent
deterioration in the cleaning performance of the cleaning blade for
cleaning the resist marks transferred onto the intermediate transfer
medium 40.

[0133]Next, a third embodiment of the present invention will be described.
The third embodiment can be practiced by the same configuration as those
of the first and second embodiments. Also in the third embodiment, at the
execution time of the first type recording medium image forming mode, the
removal amount of the carrier on the intermediate transfer member 40 is
increased as compared to the removal amount in the second type recording
medium image forming mode. To this end, in the third embodiment, when
executing the first type recording medium image forming mode, the image
carrier squeezing rollers 13Y, 13M, 13C, and 13K provided immediately
upstream relative to the primary transfer nips of the image carriers of
respective colors are used to remove a larger amount of carrier than in
the second type recording medium image forming mode and thus to increase
the removal amount of the carrier on the intermediate transfer member 40.
The same carrier removal condition as in this first type recording medium
forming mode may be applied to the color shift compensation mode.

[0134]An example of conditions at the execution time of the first and
second type recording medium image forming modes set for practicing the
third embodiment using the configuration of FIG. 1 is shown in the
following Table 3.

[0135]An example of conditions at the execution time of the first and
second type recording medium image forming modes set for practicing the
third embodiment using the configuration of FIG. 4 is shown in the
following Table 4.

[0136]In the second type recording medium image forming mode, the image
carrier squeezing rollers 13Y, 13M, 13C, and 13K are controlled to be
rotated at the same peripheral rotation speed as that of the image
carriers 10Y 10M, 10C, and 10K. On the other hand, in the first type
recording medium image forming mode, the image carrier squeezing rollers
13Y, 13M, 13C, and 13K are controlled to be rotated at a peripheral
rotation speed higher than that of the image carriers 10Y, 10M, 10C, and
10K so as to increase the removal amount of the carrier on the image
carriers 10Y, 10M, 10C, and 10K and thus to increase the removal amount
of the carrier on the intermediate transfer member 40 as compared to the
removal amount in the second type recording medium image forming mode.
The same carrier removal condition as in this first type recording medium
image forming mode may be applied to the color shift compensation mode.

[0137]Although not shown, a configuration may be adopted in which, in the
second type recording medium image forming mode, the image carrier
squeezing rollers 13Y, 13M, 13C, and 13K are controlled to be rotated in
the same direction as the rotation direction of the image carriers 10Y,
10M, 10C, and 10K at the respective nip portions, while in the first type
recording medium image forming mode, the image carrier squeezing rollers
13Y, 13M, 13C, and 13K are controlled to be rotated in the reverse
direction to the rotation direction of the image carriers 10Y, 10M, 10C,
and 10K at the respective nip portions so as to increase the removal
amount of the carrier on the image carriers 10Y, 10M, 10C, and 10K and
thus to increase the removal amount of the carrier on the intermediate
transfer member 40 as compared to the removal amount in the second type
recording medium image forming mode. The same carrier removal condition
as in this first type recording medium image forming mode may be applied
to the color shift compensation mode.

[0138]Further, in the first type recording medium image forming mode, the
image carrier squeezing rollers 13Y, 13M, 13C, and 13K may be controlled
to be rotated at a peripheral rotation speed higher than the rotation
speed of the image carriers 10Y, 10M, 10C, and 10K in the reverse
direction to the rotation direction of the image carriers 10Y, 10M, 10C,
and 10K at the respective nip portions. The same carrier removal
condition as in such a first type recording medium image forming mode may
be applied to the color shift compensation mode.

[0139]As described above, according to the third embodiment of the present
invention, since the color shift compensation mode is executed under the
same condition as in the first type recording medium image forming mode
in which the removal amount of the carrier on the intermediate transfer
member 40 is increased as compared to the removal amount in the second
type recording medium image forming mode, the position information of the
resist marks can be accurately acquired without deterioration in the
accuracy of the resist mark detection results obtained by the optical
sensor, thereby achieving accurate color shift compensation. Further, in
the present embodiment, the carrier collected by the image carrier
squeezing rollers 13Y, 13M, 13C, and 13K can be reused, achieving
effective use of the liquid developer. Further, since the color shift
compensation mode is executed under the same condition as in the image
forming mode provided in the image forming apparatus in terms of the
removal amount of the carrier on the intermediate transfer member 40, it
is possible to prevent deterioration in the cleaning performance of the
cleaning blade for cleaning the resist marks transferred onto the
intermediate transfer medium 40. That is, according to the present
invention, there can be provided an image forming apparatus capable of
achieving both the prevention of deterioration in the resist mark
detection accuracy and prevention of deterioration in the cleaning
performance with respect to the intermediate transfer member in a
balanced manner.

[0140]Next, a fourth embodiment of the present invention will be
described. FIGS. 6 and 7 are views showing main components constituting
an image forming apparatus according to the fourth embodiment of the
present invention, and FIG. 8 is a cross-sectional view showing main
components of an image forming section and developing unit in the fourth
embodiment of the present invention.

[0141]In the third embodiment, each squeezing unit corresponding to each
of the image carriers 10Y, 10M, 10C, and 10K has one image carrier
squeezing roller, while in the present embodiment, each squeezing unit
has two image carrier squeezing rollers. That is, in the image forming
apparatus according to the present embodiment, image carrier squeezing
rollers 13Y', 13M', 13C', and 13K' are provided in addition to the image
carrier squeezing rollers 13Y, 13M, 13C, and 13K. Further, in the present
embodiment, the image carrier squeezing rollers 13Y, 13M, 13C, and 13K
are arranged so as to freely abut and separate thereon from the image
carriers 10Y, 10M, 10C, and 10K.

[0142]Also in the fourth embodiment, at the execution time of the first
type recording medium image forming mode, the removal amount of the
carrier on the intermediate transfer member 40 is increased as compared
to the removal amount in the second type recording medium image forming
mode. To this end, in the fourth embodiment, when executing the first
type recording medium image forming mode, the image carrier squeezing
rollers 13Y, 13M, 13C, and 13K that have been separated from the image
carriers 10Y, 10M, 10C, and 10K in a normal state are brought into
abutting the image carriers 10Y, 10M, 10C, and 10K to remove a larger
amount of carrier on the image carriers 10Y, 10M, 10C, and 10K than in
the second type recording medium image forming mode and thus to increase
the removal amount of the carrier on the intermediate transfer member 40.
The same carrier removal condition as in this first type recording medium
forming mode may be applied to the color shift compensation mode. An
example of conditions at the execution time of the first and second type
recording medium image forming modes in the fourth embodiment is shown in
the following Table 5.

[0143]Further, in the first type recording medium image forming mode, the
image carrier squeezing rollers 13Y, 13M, 13C, and 13K brought into
abutting the image carriers may be controlled to be rotated at a
peripheral rotation speed higher than that of the image carriers 10Y,
10M, 10C, and 10K so as to increase the removal amount of the carrier on
the image carriers 10Y, 10M, 10C, and 10K and thus to increase the
removal amount of the carrier on the intermediate transfer member 40 as
compared to the removal amount in the second type recording medium image
forming mode. The same carrier removal condition as in this first type
recording medium image forming mode may be applied to the color shift
compensation mode.

[0144]Further, in the first type recording medium image forming mode, the
image carrier squeezing rollers 13Y, 13M, 13C, and 13K brought into
abutting the image carriers may be controlled to be rotated in the
reverse direction to the rotation direction of the image carriers 10Y,
10M, 10C, and 10K at the respective nip portions so as to increase the
removal amount of the carrier on the image carriers 10Y, 10M, 10C, and
10K and thus to increase the removal amount of the carrier on the
intermediate transfer member 40 as compared to the removal amount in the
second type recording medium image forming mode. The same carrier removal
condition as in this first type recording medium image forming mode may
be applied to the color shift compensation mode.

[0145]Further, in the first type recording medium image forming mode, the
image carrier squeezing rollers 13Y, 13M, 13C, and 13K brought into
abutting the image carriers may be controlled to be rotated at a
peripheral rotation speed higher than the rotation speed of the image
carriers 10Y, 10M, 10C, and 10K in the reverse direction to the rotation
direction of the image carriers 10Y, 10M, 10C, and 10K at the respective
nip portions. The same carrier removal condition as in such a first type
recording medium image forming mode may be applied to the color shift
compensation mode.

[0146]As described above, according to the fourth embodiment of the
present invention, since the color shift compensation mode is executed
under the same condition as in the first type recording medium image
forming mode in which the removal amount of the carrier on the
intermediate transfer member 40 is increased as compared to the removal
amount in the second type recording medium image forming mode, the
position information of the resist marks can be accurately acquired
without deterioration in the accuracy of the resist mark detection
results obtained by the optical sensor, thereby achieving accurate color
shift compensation. Further, in the present embodiment, the carrier
collected by the image carrier squeezing rollers 13Y, 13M, 13C, and 13K
can be reused, achieving effective use of the liquid developer. Further,
since the color shift compensation mode is executed under the same
condition as in the image forming mode provided in the image forming
apparatus in terms of the removal amount of the carrier on the
intermediate transfer member 40, it is possible to prevent deterioration
in the cleaning performance of the cleaning blade for cleaning the resist
marks transferred onto the intermediate transfer medium 40.

[0147]As a reference, an example of parameters in image forming processes
in the first and second type recording medium image forming modes are
shown in the following Table 6.

[0148]There is a case where a mode (low-speed mode) in which the moving
speed of the intermediate transfer member 40 and speed of various
processes associated with the intermediate transfer member 40 are made
lower than the speed of an ordinary printing speed in accordance with the
paper type (especially, thickness of the paper) is provided. However,
such a low-speed mode is not applied to the color shift compensation mode
of the present invention. That is, in order to execute the color shift
compensation mode, the moving speed of the intermediate transfer member
40 needs to be the same in each of a plurality of image forming modes
provided in the image forming apparatus. This is because that the
condition for the color shift compensation changes in accordance with the
moving speed of the intermediate transfer member 40.

[0149]As a reference, an example of parameters in the low-speed mode image
forming process is shown in the following Table 7.

[0150]Next, a fifth embodiment of the present invention will be described.
FIGS. 9 and 10 are views showing main components of a developing unit in
the image forming apparatus according to the fifth embodiment of the
present invention. The present embodiment can be practiced in parallel
with the embodiments described above.

[0151]In the color shift compensation mode of the present embodiment, the
carrier contained in the resist marks is removed while the removal amount
thereof is controlled so as not to be excessive. More specifically, as in
the case of the above embodiments, the color shift compensation mode is
executed under a condition of the same carrier removal amount as in the
image forming mode in which the removal amount of the carrier on the
intermediate transfer member 40 is largest of all the image forming modes
provided in the image forming apparatus.

[0152]In the present embodiment, as a plurality of image forming modes
provided in the image forming apparatus, those in which toner consumption
amount for use in an image forming process differs from one another can
be adopted. More specifically, the image forming apparatus according to
the fifth embodiment has a normal printing mode and a toner-saving
printing mode in which an image forming process is carried out with a
smaller toner amount than in the normal printing mode.

[0153]In the toner-saving printing mode, the amount of a liquid developer
supplied from the anilox roller 32 to the developing roller 20 is
controlled to be reduced as compared to that in the normal printing mode.
The carrier amount on the intermediate transfer member 40 is proportional
to the supply of the liquid developer. Thus, in the present embodiment,
the same carrier condition as in the toner-saving printing mode is
applied to the color shift compensation mode.

[0154]A method of controlling the amount of the liquid developer supplied
from the anilox roller 32 to developing roller 20 will be described with
reference to FIGS. 9A and 9B by taking the developing unit of yellow as
an example. Since the developing units of respective colors have the same
configuration, only the developing unit of yellow will be described
below.

[0155]In the example of FIGS. 9A and 9B, in order to control the amount of
the liquid developer supplied from the anilox roller 32Y to developing
roller 20Y, the pressing force of the restricting blade 33Y is changed.
More specifically, assuming that the pressing force of the restricting
blade 33Y in the normal printing mode is F1 and pressing force thereof in
the toner-saving printing mode is F2, F2 is set larger than F1 to thereby
reduce the amount of the liquid developer supplied from the anilox roller
32Y to developing roller 20Y at the execution time of the toner-saving
printing mode.

[0156]Another method of controlling the amount of the liquid developer
supplied from the anilox roller 32 to developing roller 20 will be
described with reference to FIGS. 10A and 10B.

[0157]In the example of FIGS. 10A and 10B, in order to control the amount
of the liquid developer supplied from the anilox roller 32Y to developing
roller 20Y, the rotation speed of the anilox roller 32Y is changed. More
specifically, assuming that the peripheral speed of the anilox roller 32Y
in the normal printing mode is V1 and peripheral speed thereof in the
toner-saving printing mode is V2, V1 is set larger than V2 to thereby
reduce the amount of the liquid developer supplied from the anilox roller
32Y to developing roller 20Y at the execution time of the toner-saving
printing mode.

[0158]The methods described using FIGS. 9 and 10 can be used in a combined
manner so as to control the amount of the liquid developer supplied from
the anilox roller 32Y to the developing roller 20Y.

[0159]In the manner as described above, the amount of the liquid developer
supplied for the image forming process is reduced in the toner-saving
printing mode as compared to that in the normal printing mode and,
correspondingly, the carrier amount on the intermediate transfer member
40 is reduced. In the present embodiment, the same condition as in this
toner-saving printing mode is applied to the color shift compensation
mode.

[0160]As described above, according to the fifth embodiment of the present
invention, since the color shift compensation mode is executed under the
same condition as in the toner-saving printing mode in which the carrier
amount on the intermediate transfer member 40 is reduced as compared to
the carrier amount in the normal printing mode, the position information
of the resist marks can be acquired without deterioration in the accuracy
of the resist mark detection results obtained by the optical sensor,
thereby achieving accurate color shift compensation. Further, since the
color shift compensation mode is executed under the same condition as in
the image forming mode provided in the image forming apparatus in terms
of the amount of the carrier on the intermediate transfer member 40, it
is possible to prevent deterioration in the cleaning performance of the
cleaning blade for cleaning the resist marks transferred onto the
intermediate transfer medium 40. That is, according to the present
invention, there can be provided an image forming apparatus capable of
achieving both the prevention of deterioration in the resist mark
detection accuracy and prevention of deterioration in the cleaning
performance with respect to the intermediate transfer member in a
balanced manner.

[0161]As a reference, an example of parameters in the image forming
process of the toner-saving printing mode is shown in the following Table
8.

[0162]The processing performed in the color shift compensation mode will
be described in more detail below. FIG. 12 is a view showing a flowchart
of the color shift compensation mode processing. As shown in FIG. 12,
after the start of the color shift compensation processing, calibration
of the optical sensor 90 for detecting the resist marks are performed to
adjust the light-emitting amount of the sensor such that the surface
output of the intermediate transfer member 40 assumes a predetermined
voltage. Then, the condition of the carrier removal amount is set to the
first condition which is the same condition as in the first type
recording medium image forming mode.

[0163]Subsequently, the resist marks are formed on the intermediate
transfer member 40, and the formed resist marks are detected using the
optical sensor 90. Main-scanning direction resist displacement amounts,
sub-scanning direction resist displacement amounts, and skew amounts are
calculated from the detection results of the resist marks and then, based
on the calculated values, resist compensation amounts (the main-scanning
direction resist compensation values, sub-scanning direction resist
compensation values, and skew compensation values) are set for respective
colors.

[0165]Calculation methods of the main-scanning direction resist
displacement amount, sub-scanning direction resist displacement amount,
and skew amount will be described. The resist displacement amount and
skew amount for each color can be calculated from detection result (edge
time information) of a predetermined resist mark. The following
description is made for a case where K (black) is set as a reference
color.

[0166]Main-Scanning Direction Displacement Amount Calculation Method

[0167]The main-scanning direction resist displacement amount can be
calculated from a detection result of a mark obtained by combining a
straight line and diagonal line. The following Table 9 explains an
example of parameters when black (K) is set as a reference. FIG. 15 is a
view showing a sensor output observed when resist marks are detected by
means of the optical sensor 90.

[0168]First, the time pitches between the straight lines and diagonal
lines of respective colors are calculated from the detection results of
the resist marks, i.e., time information concerning the edges of the
resist marks in the following manner.

Lk={(t3-t1)+(t4-t2)}/2

Lc={(t7-t5)+(t8-t6)}/2

Lm={(t11-t9)+(t12-t10)}/2

Ly={(t15-t13)+(t16-t14)}/2

[0169]Then, the main-scanning direction resist displacement amounts of
respective colors with respect to the reference color (in this case, K)
are calculated from the time pitches of the respective colors in the
following manner.

Dc=Lc-Lk

Dm=Lm-Lk

Dy=Ly-Lk

[0170]Resist compensation values are set based on the resist displacement
amounts and, based on the compensation values, the main-scanning
direction light-emitting positions of the exposure units such as a line
head (LED, OPH) other than the reference color are changed to compensate
the main-scanning direction resist displacement.

[0171]Sub-Scanning Direction Displacement Amount Calculation Method

[0172]The sub-scanning direction resist displacement amount can be
calculated from a detection result of a straight line mark. The following
Table 10 explains an example of parameters when black (K) is set as a
reference. FIG. 16 is a view showing a sensor output observed when resist
marks are detected by means of the optical sensor 90.

[0173]First, the time pitches between the resist marks of the respective
colors and that of the reference color are calculated from the detection
results of the resist marks, i.e., time information concerning the edges
of the resist marks in the following manner.

Pc=((t3-t1)+(t4-t2))/2

Pm=((t5-t1)+(t6-t2))/2

Py=((t7-t1)+(t8-t2))/2

[0174]Then, the sub-scanning direction resist displacement amounts of
respective colors are calculated from the time pitches of the respective
colors and design values in the following manner.

Rc=Pc-pc

Rm=Pm-pm

Ry=Py-py

[0175]Resist compensation values are set based on the resist displacement
amounts and, based on the compensation values, the sub-scanning direction
light-emitting timings of the exposure units such as a line head (LED,
OPH) other than the reference color are changed to compensate the
sub-scanning direction resist displacement.

[0176]Skew Amount

[0177]The skew amount of each color can be calculated from a detection
result of sub-scanning direction resist marks formed on both ends of the
intermediate transfer belt 41. The following table 11 explains an example
of parameters when black (K) is set as a reference. FIG. 17 is a view
schematically showing a state where resist marks are detected by means of
an optical sensor 90. In this case, two sensor outputs from a front side
sensor and rear side sensor provided on one side of the roller and the
like in the shaft direction thereof are used.

[0178]The time pitches between the resist marks of the respective colors
and that of the reference color are calculated from the time information
concerning the edges of the resist marks which are obtained at both ends
(front side and rear side) of the intermediate transfer member 40 in the
direction perpendicular to the moving direction thereof, and the skew
amounts are calculated based on a difference between the time pitches at
the both ends of the intermediate transfer belt 41 in the following
manner.

Sc=Pcf-Pcr

Sm=Pmf-Pmr

Sy=Pyf-Pyr

[0179]Skew compensation values are set based on the skew amounts and,
based on the compensation values, the sub-scanning direction
light-emitting timings of the exposure units such as a line head (LED,
OPH) other than the reference color are changed for each chip or for each
dot to compensate the skew.

[0180]Although the present invention has been described with reference to
the various embodiments, an embodiment obtained by arbitrarily combining
a part or all of the configurations of the above embodiments is included
in the scope of the present invention.